This invention relates to the field of particle concentrators, and more particularly to an apparatus and method for capturing and transporting to an analyzer target chemical substances adherent to a substrate that either has been rubbed on the surface of a test subject to test for the presence of the target chemical substances or has been exposed to a vapor. Preconcentration of the target substances results from the accumulation of the substrate on the test surface. Specifically, according to the invention, target substances thus preconcentrated are removed (or, as the term is used herein, “evolved”) from the substrate by heating the substrate in the presence of suction or other gas flow for movement to a chemical analyzer such as a portable ion mobility spectrometer. Resistive heating is accomplished by passing current through the metallic substrate. For purposes of this disclosure, including the appended claims, “suction” in association with the chemical analyzer is intended to include all modalities through which gases are caused to pass from outside of the analyzer to inside the analyzer, regardless of whether the fan or other means for causing the flow of gases into the analyzer resides inside the analyzer or external to it. The apparatus of the invention is suited to human portability and is especially useful in conjunction with detecting compounds such as explosives, illegal drugs, other controlled substances and chemical agents. For purposes of this application, in the context of describing the claimed invention, the term particle is intended not to exclude vapor.
Additional background information, supplemental to the information provided here, is found in U.S. Pat. No. 5,854,431 “Particle Preconcentrator”, U.S. Pat. No. 6,085,601 “Particle Preconcentator”, and in pending U.S. patent application Ser. No. 09/339,349, now U.S. Pat. No. 6,523,393 “Human Portable Preconcentrator System”, all of which are incorporated by reference herein in their entirety.
The detection of explosives, narcotics or other chemicals is a growing part of contraband detection. Recent years have seen rapid development of detectors capable of identifying the presence of explosives by capturing and identifying either vapors emanating from explosive materials or particles of explosive material, or both. Similarly, such detectors can also identify vapors and particles associated with other forms of contraband such as illegal drugs and other controlled substances. Such vapors and particles associated with contraband may be present and detectable on or near persons or objects that have been exposed to contraband materials and substances. Suitable detectors for this purpose include, but are not limited to, ion mobility spectrometers (IMS), electron capture detectors, mass spectrometers (MS), and chemiluminescence-based systems.
Detection of explosives, narcotics or other contraband substances demands reliable and convenient means for collecting and analyzing sample. The '431, '601 and '393 patents mentioned above are examples of ways to collect trace amounts of target chemical in dilute concentration in gases. The present invention provides an efficient, portable system for either detecting the swiped substances or for collecting vapor samples and subsequently detecting those samples.
Swiping surfaces in order to concentrate sample is well known in the art of chemical detection. However, a challenge remains in how to reliably analyze chemicals collected and concentrated using the swiping approach, especially so that analysis results can be obtained quickly in a field setting. The present invention offers a quick and reliable method and apparatus to capture the target chemicals collected using the swiping technique and to deliver those chemicals to an analyzer for detection. An important aspect of the invention is that heat is used in a controlled fashion to drive off chemicals adherent to the swiped substrate. For purposes of this disclosure, the term “evolve” is used in conjunction with the process whereby target chemicals are driven off of the substrate as a consequence of application of heat.